Sun’s annual transit through Aquarius (kumbha) is named as Maasi or Magha month. Sun’s direct aspect falls on the sign of Leo and the full moon of this month will fall on magha nakshatra thus the name. Theme of this month would be achieving the next level in your life. Because magha is all about attaining the throne. It’ll bring results for your efforts. For ex. If your last month was spent on researching a topic then this month would be spent on attaining the conclusion. This month is good for worshipping Lord Shiva as Aquarius is the sign of Rudra and Ardhanareeshwara. Aquarius starts with dhanishta (lioness) and ends with purva bhadrapada (lion) and Leo sign itself is a lion so it will bring success in whatever you especially if your Sun, Leo and Aquarius are supporting your efforts. Your thought process may also change and become profound in this time. Aquarius pot (kumbha kalash) has divine significance in vedic culture thus it is kept on top of temple towers in Hindu temples around the world.
People who want to perform remedy for Lord Shiva can also use this month to gain more power. Although the entire month is best for religious and spiritual activities, some days are more powerful than the others, especially trayodashi and chaturdashi tithis. Maha Shivratri aka Great night of God Shiva is one of the important annual religious festivals celebrated by Shiva worshippers (Shaivites) across the world. This night is celebrated on krishna paksha chaturdashi tithi of this month. Chanting Shiva mantras (panchakshara, mrityunjaya), pouring milk on Shivlinga (milk abhishekam) etc. are auspicious and powerful remedies. Worshippers will stay awake at Shivratri night and chant mantras and perform pujas the entire night for Shiva. Some may also perform yogic practices while chanting mantras to gain tantric powers.
Maasi Magha (மாசி மகம்)/Kumbhmela (கும்பமேளா)
Maasi magha/Kumbhmela, an annual festival celebrated on the full moon/purnima of this month (moon will be in magha nakshatra). Worshippers will take a holy dip in temple waters or rivers on this day and perform rites to their ancestors. People who don't have progeny will also perform special pujas to their ancestors and Gods for the blessings of children because magha is connected to pitru devatas and Leo sign is the natural 5th house of children.
Fire rituals: This month is one of the best times in a year to do fire rituals (homa/havan/yagya).
Auspicious days, nakshatras and tithis for worship
Days such as Mondays and Saturdays. Nakshatra such as Ardra, magha, purva & uttara phalguni, dhanishta and purva bhadrapada. Tithis such as trayodashi, chaturdashi, chaturthi and sashti tithis are auspicious for rituals, pujas, havans meditation, chanting mantras etc.
Note: Don't get confused with the names maasi and magha. Some call it maasi month and some call it magha month but the festival on purnima is always called maasi magha.